LONG-RANGE INTERACTION BETWEEN NONBONDED HYDRIDES - ATTRACTIVE IN THE CASE OF TRANSITION-METALS

Extended Hiickel molecular orbital calculations give a positive Mulliken overlap population between cis nonbonded dihydride and trihydrides in transition-metal complexes (i.e., m-(H)2Os(CO)4 and CpIr(PH3)(H)3+). In contrast, isolobal organic systems (CH4 and Dn CH5+, respectively) show no tendency for such a positive long-range interaction. The results are interpreted in terms of variable electron transfer from the symmetry-adapted polyhydride Hn molecular orbitals into those of the metal or organic fragment. The cause of this variation can be traced to the local symmetry properties of the cylindrical-shaped LUMO. The results are consistent with the high fluxionality of polyhydrides as well as the recently discovered phenomenon of quantum mechanical exchange in NMR. © 1990, American Chemical Society. All rights reserved.